This invention relates to a slip-controlled brake system for automotive vehicles with a brake booster which acts on a tandem master cylinder substantially consisting of a push-rod piston, an intermediate piston, as well as of a resetting arrangement, with pressure lines connecting the tandem master cylinder with the wheel brakes, with controllable multi-directional valves inserted into the pressure medium lines leading to the wheel brakes and to a pressure compensation and supply reservoir, with an auxiliary pressure source, with transducers for the detection of the rotational behavior of the wheels and with electronic circuits for the evaluation of the measured values and for the generation of valve control signals.
Known brake systems with slip control which are equipped with a tandem master cylinder the two hydraulic circuits of which are connected with the wheel brakes via operable valves. For a pressure reduction at the wheel brake cylinders for the purpose of counter-acting an imminent wheel lock-up, by means of the valves, a pressure medium line is released from the respective wheel brake cylinder to the pressure compensation or supply reservoir so as to enable hydraulic medium to run off from the hydraulic brake circuits. So as to avoid a depletion of the hydraulic volume after a repeated pressure reduction, in such systems it is necessary to dynamically supply additional hydraulic medium into the pressurized brake circuits during brake slip control.
The known systems thus require for every controlled hydraulic circuit multi-directional valves which are operable independently of one another. The energy consumption is considerable as the pressure reduction in all circuits is effected by pressure compensation towards the supply reservoir. The measures for the individual control of the braking pressure in the circuits, which are independent of one another, as well as for the generation and supply of the required hydraulic energy, which will be high in particular in unfavorable conditions as in case of icy roads or aquaplaning, thus require a substantial expenditure with regard to pumps, pressure accumulators, etc.
It is thus an object of this invention to develop a reliably working brake system with slip control, which will be up to all requirements, even in unfavorable conditions, which will need a relatively low-power auxiliary pressure source as compared to known systems, and which altogether will but need a small expenditure with regard to components and manufacture.